Like most things in life, it depends.
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I Don’t Digg Being Dugg. It is entirely possible to get twenty thousand visitors, drive up your bandwidth costs, and get zero sales. If you paid on top of it, you're in a serious hole.
However, you should have some idea of the profit potential of a page before you attempt to pay for a Digg placement. It should be well suited to the type of traffic you're likely to get. If you think you're going to get 10,000 doctors or business people from being dugg, you're need to rethink your assumptions.
However, if you have a dating book and you put up articles which get dugg, it might just pay off.
If what you paid to get on Digg, increased bandwidth costs and other costs are less than the sales increase, you make out ...if not, you don't. Such a factor is more like image advertising, where you would probably spend on a campaign, test and tweak, and not one-shots. Entirely depends on your target market, cost structure, offer, and not on whether you get on Digg.
The illusion of huge amounts of traffic seem intoxicating. But huge amounts of the wrong kinds of traffic do nothing but drive up costs. Getting dugg is not a magic solution to your marketing problems. Raw traffic is as bogus as the old idea of the "page hit."